DETRIMENTAL EFFECT OF EXCESS LECITHIN ON THE STABILITY OF FLUOROCARBON LECITHIN EMULSIONS

The formation and stability of concentrated lecithin-stabilized emulsions of perfluorodecalin (100% and 70% w/v, i.e. 51.5% and 36.1% v/v) have been studied for lecithin/fluorocarbon ratios ranging from 2 to 11. The stability was found to go through a maximum for a lecithin/fluorocarbon ratio of 4-6%. Emulsions prepared with lecithin/fluorocarbon ratios higher than 6% lead, after 5 months storage at 4, 25, and 50-degrees-C, to increasingly larger particle sizes and wider size distributions. This detrimental effect of an excess of surfactant on the emulsions' stability is shown to be related to the presence of increasing amounts of fluorocarbon-empty lecithin-based aggregates. These aggregates were identified by ESR as consisting of free lecithin vesicles.